More on asymmetric polarization
Here are some graphs to follow up on this Monkey Cage post.
UPDATE (Sept 12, 2014)
Here's another graph of the Bailey data, to illustrate the narrowing and moderate cross-time shift of the congressional GOP and northern Democratic ideal point estimates, but a more dramatic leftward cross-time shift in the congressional southern Democratic ideal point estimates.
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UPDATE (Sept 13, 2014)
Here are the do files I used to create a database with Bailey scores and state and party codes for each case (House, Senate). Here is a description of the process that I used to create the do files.